1. Field of the Invention
This invention relates to a one-piece stainless steel rim for mating a meter cover and base for an electric meter and particularly to a method of making the rim and attaching it to the cover. The invention is particularly suitable for an electric induction watthour meter.
2. Description of the Prior Art
For many years, a stainless steel rim has been used to attach to the molded glass cover to the base of a single phase watthour meter. The circular flanged rim is assembled to the cover by welding clips onto the rim. During the welding process, the cover which is part of the assembly, is prone to breakage due to forces applied to the metal parts to keep them on location and heat generated during welding. Large variations in the dimensions of the molded cover also aggravate the assembly process causing non-uniform loading to be applied to the glass that may cause injury to a person during assembly. Metal rims, being made from thin coil stock, have sharp edges which can cause injury to a person when assembling the cover onto the base or the insertion of the complete meter into the socket. Upon insulation of the meter in the field, the installer takes the meter and inserts it into a socket and then places a xe2x80x9cU-shapedxe2x80x9d sealing ring around the perimeter of the cover flange, rim and base. To make sure that the sealing ring fits over the assembly, the diameter and height build up of the meter, rim and base are dimensioned to meet specific ANSI-limits. The sealing ring also has ANSI-values limiting its size. Any change in the design of the rim, cover or base may adversely impact the fit of the sealing ring over the assembly. It has heretofore been proposed to replace metal rims with a plastic mating ring for mounting a meter cover to a meter base. Examples of such plastic mating rings are disclosed in U.S. Pat. No. 5,499,159 and U.S. Pat. No. 5,959,243. While such plastic rings have been successful, nevertheless they have left something to be desired. Since plastic mating rims are endless rings, their circumference must be closely controlled with respect to the circumference of the meter cover and the diameter must not exceed ANSI limits. Also, plastic tends to deteriorate with time and under adverse conditions. Plastic rims must be of sufficient strength that they will not broken in normal handling. Also the plastic rims should not be deflexible so that they can be pulled off the cover or the rim be pulled off of the base when the meter is being removed from the socket by the meter installer. The design of the rim whether metal or plastic must be adequate to compensate for the variation in the stack build up of the cover, base and gasket to provide both for the sealing of the gasket and limiting the torque required to turn the rim-cover assembly onto the base.
It would be desirable to reduce the complexity of the assembly of the mating rim with a meter cover and base by making the rim from a single strip of stainless steel sheet metal. It would also be desirable to form the various features of the rim from the rim material and thus reduce the cost associated with the manufacture of the part and the assembly of the rim onto the cover. It would also be desirable to construct the rim so that no additional components are required as attachments to the rim to make it a functional assembly and also to eliminate all welding. The basic structural features required in the rim are (1) tabs for interlocking the rim to the cover (2) locking lugs to allow the rim to be tightened onto the base and (3) a means of securely attaching one end of the rim to the other. It would be desirable for these structural features to be punched out from the rim itself and thus an integral part of it. All of these structural elements are bent radially inward from punched and lanced sections in the rim. Since all of the elements are die punched and bent sections, a high degree of dimensional accuracy is maintained between elements. All of the elements on the periphery of the rim are precisely located relative one to the other. When the rim is attached to the cover, the overall length of the rim controls the diameter of the rim. Variations in the diameter of the rim are greatly minimized and the fit between the rim and the cover is closely controlled. A simple process of upsetting the locking tabs is only required for completing the attachment. No welding is required.
It is an object of the present invention to provide a one-piece stainless steel rim in which all of the tabs for interlocking the rim to the cover and the locking lugs for attachment to the base are formed from the rim itself thereby eliminating the need for any spot welding.
It is a further object of the invention to enable the rim to be assembled onto the glass cover by fitting it over the periphery of the cover flange and making the attachment by upsetting two locking tabs. It is a further object of the invention to construct the locking lugs with flexible sections to control the magnitude of the twisting torque required to rotate the rim-cover assembly onto the base.
In accordance with the present invention there is provided a method of making a one-piece stainless steel rim for mating a meter cover and base. The method comprises the steps of cutting a strip of stainless steel of predetermined width to a predetermined length corresponding to the circumference of the meter cover and forming a flange on one edge of the strip. The method further includes the step of punching a plurality of attachment tabs in the strip at spaced locations, the attachment tabs being spaced apart from the flange to receive therebetween an annular flange on the meter cover. The method further includes the step of punching a plurality of locking lugs in the strip at spaced locations, the locking lugs being spaced apart from the flange to receive therebetween an annular flange on the meter base. The method further includes the step of punching a pair of locking tabs at one end of the strip and punching an opening in the opposite end of the strip to receive the locking tabs. The method further includes the step of bending the plurality of attachment tabs, the plurality of locking lugs and the pair of locking tabs to the same side of the strip as the flange, forming the strip into a circular ring and securing the ends of the rim together by inserting the locking tabs into the opening at the opposite end of the rim and mechanically securing one end of the rim to the other.
Further in accordance with the invention there is provided a one-piece stainless steel rim for mating a meter cover and base comprising a strip of stainless steel of predetermined width cut to a predetermined length corresponding to the circumference of the meter cover, a flange formed on one edge of the strip, a plurality of attachment tabs punched in the strip at spaced locations, the attachment tabs being spaced apart from the flange to receive therebetween an annular flange on the meter cover, a plurality of locking lugs punched in the strip at spaced locations, the locking lugs being spaced apart from the flange to receive therebetween an annular flange on the meter base, a pair of locking tabs punched in the strip at one end thereof, an opening punched in the opposite end of the strip to receive the locking tabs, the plurality of attachment tabs, the plurality of locking lugs and the pair of locking tabs being bent to the same side of the strip as the flange, the strip being formed into a circular rim, and the ends of the rim being secured together by inserting the locking tabs into the opening at the opposite end of the rim.
For more detailed disclosure of the invention and for further objects and advantages thereof, reference is to be had to the following description taken in conjunction with the accompanying drawings.